The present invention relates to cryogenic thermometry and more particularly to the use of molecular luminescence in the determination of cryogenic temperatures.
Temperature measurement in the cryogenic region is presently done generally using either the measurement of the vapor pressure of liquid halium, or by means of a calibrated resistance as a sensor. In the helium method, the vapor pressure is measured and a conversion of the helium vapor pressure to its temperature is made using a suitable conversion table (F. G. Brickwedde, J. Res. NBS 64A, 1960). This system has a distinct advantage in that the temperature determination is based on thermodynamic properties of a pure sensor material, and thus a single calibration can be used for all individual sensors. On the other hand, the apparatuses involved for obtaining the vapor pressure measurements are cumbersome, and measurements are tedious. Further, the low critical temperature of helium limits these measurements to below 5.3K.
In the resistance method, as well-defined current is passed through a calibrated resistance (carbon glass, germanium, silicon diode) whose resistance varies with temperature. The voltage across the resistance is measured and is converted to sensor temperature by use of a calibration curve or table. The resistance method is considerably more convenient to use than the helium method and can be used throughout the liquid helium range as well as above 5.3 K. However, since no two sensors can be constructed alike, each resistance element must be calibrated individually, usually by comparison with a secondary standard whose calibration can be traced to primary temperature standards maintained at the National Bureau of Standards.